高分子報告
Membrane reactor
班級:化材三乙
姓名:王冠智
學號:49940103
一、 原理說明:
Abstract
Palladium can play an interesting role as a catalytic membrane,
that is, a hydrogen separative and catalytically active
wall. Utilizing this function, a palladium membrane reactor
capable of working under an adiabatic condition was designed in
this study for coupling two conjugated reactions. On one side of
the membrane, dehydrogenation of cyclohexane as a model
takes place in the catalyst-packed layer, and on the membrane
surface of the other side hydrogen permeated reacts in-situ
with oxygen. In the adiabatic membrane reactor, a heat
compensation between the endothermic dehydrogenation and the
exothermic oxidation is expected to be realized. As a result, it
became obvious experimentally that the generated heat due to
the oxidation refluxed to the dehydrogenation side, heated up the
catalyst layer and therefore enhanced the dehydrogenation.
A simple mathematical model derived for analyzing the reaction
process could simulate the practical reactor performances
well.
A dehydrogenation reaction of the form A ¢~ B + H2 was simulated in a
cocurrent, isothermal, membrane-enclosed catalytic
reactor to study the effects of reactant permeation rate,
hydrogen-permeation selectivity, feed composition, and reactant space
times on reaction conversion. Two dimensionless numbers, the
Damkohler number and the permeation number, were used to
quantify the effects of reactant space time and reactant loss on conversion
respectively. The Damkohler number is the ratio of
maximum reaction rate to inlet reactant flow rate, and the permeation
number is the ratio of maximum reactant permeation rate
to inlet reactant flow rate. For reactant space times at STP between 0.3
and 30 s, and hydrogen-permeation selectivities between
3 and 1000, conversion decreased as the maximum reactant permeation
rate exceeded the inlet reactant flow rate because reactant
loss controlled conversion. For hydrogen-permeation selectivities
between 3 and 40, a membrane reactor gave maximum
conversions when the maximum reactant permeation rate equaled the
inlet reactant flow rate, and the reactant space times at STP
had to be greater than 1.5 s to obtain conversions higher than the
enhanced equilibrium conversion due to dilution by the inert
sweep gas.
Keywords: Membrane reactor; Dehydrogenation; Modeling; Reactant loss;
Membrane selectivity
Keywords: Palladium; Membrane reactors; Metal membrane; Reaction
coupling; Catalytic membrane
應用用途:
Fig. l shows a sectional view of a palladium
membrane reactor designed to conduct an adiabatic
operation. The adiabatic membrane reactor is a type
of vacuum bottle inside which a double-tube type of
membrane reactor is placed. The annular space between
the outer stainless-made shell and the membrane
reactor can be evacuated with a rotary pump to
prevent heat loss by convection from the reactor to
the outside as much as possible.
A one-end closed Pd77Ag23 tube, 0.2 mm thick,
190 mm long and 10 mm in inner diameter, used as
the membrane is connected to the reactor body by
welding with silver solder. In the annulus around the
membrane tube cylindrical 0.5 wt% Pt/A120 3 pellets,
supplied by N.E. Chemcat (3.3 rnm ~ × 3.6 mm,
86.7 g), are uniformly packed. Four CA thermocoupies,
TC-2-TC-5, are inserted at different points in
the reactor as shown in Fig. 1 to follow the temperature
changes. The adiabatic membrane reactor is
The experimental run is started with an isothermal
reaction mode. The feed, cyclohexane, in the range
2.16 to 8.87 mg/min is injected with a micro-syringe
pump to a vaporizer and then transferred to the
catalyst layer of the reactor (160 cm 3 in superficial
volume) together with helium gas as a diluent, the
flow rate of which is regulated with a mass-flow
controller (MFC). The resulting initial concentration
of cyclohexane and GHSV were respectively in the
range 5.77 to 21.1 vol% and 1.13 to 4.62 h. To the
separation side of the membrane reactor (inside the
membrane tube) sweep gas (Ar) is introduced at a
constant flow rate through an MFC. The conversion
of cyclohexane to benzene is determined based on
gas chromatographic analysis.
After the result of the gas analysis under the
isothermal condition becomes almost steady (usually
after 3-4 h), an adiabatic reaction mode is started by
exchanging the sweep gas from argon to an oxygencontaining
gas (15.1% 0 2 in Ar or dry air) as well as
by evacuating the gas inside the outer shell. Changes
in temperature inside the reactor are continuously
recorded. The production rate of water on the sweep
side is obtained from the amount of water trapped
with a silica-gel packed column for a period of 3-4
h. Also the amount of oxygen consumed on the
sweep side is determined by gas chromatography.
The catalytic oxidation (or surface combustion) of
hydrogen with oxygen on the palladium-membrane
surface is carried out under an isothermal mode,
where pure hydrogen (36-68 cc/min) is supplied to
the catalyst-packed side, oxygen (dry air, 10-74
cm3/min) to the inner side of the membrane tube.
All data are taken after the system reaches a steady
state.
二、 參考文獻: